Method for casting polymeric gels from volatile mixtures of monomer in open molds

Abstract

The invention pertains to apparatus for casting polymeric gels from volatile mixtures of monomers in open molds. The principle of the invention resides in the fact that the same concentrations of volatile components present in the polymerization mixture are also present in the gaseous state within a protective gas maintained above the free surface of the polymerization mixture, the gaseous volatile components being in the equilibrium state with those in the polymerization mixture at polymerization temperature. The apparatus includes a main pipe branch which introduces a pure protective gas into a polymerization apparatus and at least one auxiliary pipe branch for saturating the protective gas with a volatile component. These main and auxiliary pipe branches are formed by an inlet pipe connected to a control valve for setting a constant volume flow-rate and further leading to a device for measurement of the flow rate, where their outlet pipes are connected to a common inlet entering the polymerization apparatus and a saturator for a pure volatile component of the monomer mixture is arranged within the auxiliary branch before the outlet pipe.

We claim: 
     
       1. Apparatus for casting a polymeric gel into a contact lens in an open mold from a liquid polymerization mixture containing at least one volatile monomer component dissolved therein in which a protective gas is provided above the open surface of the polymerization mixture during polymerization, said protective gas prior to coming into contact with said open surface of the polymerization mixture being combined with an amount of said volatile monomer which will be in equilibrium with the volatile monomer present within the polymerization mixture under polymerization conditions, said apparatus comprising: (a) a polymerization unit containing at least one open mold having an optical surface for casting a contact lens;   (b) a first conduit for introducing a controlled flow of protective gas to a common conduit (d); and,   (c) a second conduit for introducing a controlled flow of protective gas containing said volatile monomer into said common conduit (d), said common conduit (d) introducing the protective gas received from first conduit (b) and the protective gas containing said volatile monomer received from second conduit (c) into polymerization unit (a).   
     
     
       2. The apparatus of claim 1 wherein the polymerization unit includes means for rotating the mold during polymerization. 
     
     
       3. The apparatus of claim 1 wherein each of first conduit (b) and second conduit (c) includes means for providing a constant volume flow rate and means for measuring said flow rate. 
     
     
       4. The apparatus of claim 3 wherein second conduit (c) includes means for introducing volatile monomer into the protective gas. 
     
     
       5. The apparatus of claim 4 wherein said means for introducing volatile monomer into the protective gas is a saturator. 
     
     
       6. The apparatus of claim 4 wherein said means for introducing volatile monomer into the protective gas is positioned between the means for measuring said flow in second conduit (c) and the point where second conduit (c) meets common conduit (d). 
     
     
       7. The apparatus of claim 1 wherein common conduit (d) is provided as an extension of first conduit (b).